 
 (defn- tree-map-append [left right]
   (cond
-    (coercive-= left nil)
+    (nil? left)
     right
 
-    (coercive-= right nil)
+    (nil? right)
     left
 
     (instance? RedNode left)

                editable))))
        (let [key-or-nil  (aget arr (* 2 idx))
              val-or-node (aget arr (inc (* 2 idx)))]
          (cond (coercive-= nil key-or-nil)
                (let [n (.inode-assoc! val-or-node edit (+ shift 5) hash key val added-leaf?)]
                  (if (identical? n val-or-node)
                    inode

        (let [idx         (bitmap-indexed-node-index bitmap bit)
              key-or-nil  (aget arr (* 2 idx))
              val-or-node (aget arr (inc (* 2 idx)))]
          (cond (nil? key-or-nil)
                (let [n (.inode-without val-or-node (+ shift 5) hash key)]
                  (cond (identical? n val-or-node) inode
                        (not (nil? n)) (BitmapIndexedNode. nil bitmap (clone-and-set arr (inc (* 2 idx)) n))
